The present invention relates to a composition for preparing bone cement. More specifically, the present invention relates to bone cement compositions containing calcium hydroxide, a sparingly soluble strong base in an aqueous environment.
There are a number of conditions in which hard and soft tissues may be compromised due to decreased local environmental pH such as open and closed fractures, infections, decreased tissue perfusion, and disease states. Regarding these conditions, bone cement has been commonly used as a structural component, an adjuvant therapeutic agent, and a drug delivery system.
One type of bone cement is made by blending polymerizable materials such as homopolymers or copolymers of methylmethacrylate together with suitable liquid monomers, primarily methylmethacrylate, and a catalyst to form a plastic paste which is inserted into the body and cured. An example of such a bone cement is shown in British Patent No. 1,431,211, which discloses a bone cement composition having a liquid component comprising (a) at least 50% of monomeric methacrylate, up to 5% of a tertiary amine and between 10% and 45% of at least one C.sub.2 -C.sub.6 alkyl methacrylate, (b) a powder component including polymethylmethacrylate, and (c) a catalytic system such as one including dimethyl-p-toluidine. The British patent warns of the problems that can occur to the bone tissue if the temperature of the exothermic reaction of the polymer during curing rises above a critical temperature.
As a result of trauma and during the rehabilitation of bones after surgery, infection often occurs. To combat the infection, bone cements may also include antibiotics. However, because of the high temperatures caused by the polymer mixture during curing (i.e., during polymerization of polymethylmethacrylate during arthroplasty), the cytotoxicity of liquid methylmethacrylate monomer used for the polymerization, and the high toxic doses of antibiotics needed to treat bone infections, use of polymethylmethacrylate bone cement can lead to locally compromised or necrotic bone.
It is therefore an object of the present invention to provide a method for stimulating bone cell metabolism by maintaining or elevating local pH in the bone adjacent to bone cement.
Another object of the present invention is to provide a bone cement composition that ameliorates the toxic effect of an antibiotic as it is released from the bone cement composition.